This invention relates in general to the production of plywood and more particularly to a method of treating wood veneer in a manner to reduce the amount of adhesive needed to bond the veneer into plywood.
In the production of plywood, the wood veneers are dried, coated with a suitable adhesive assembled and hot pressed into plywood panels. Because the adhesive cost is a major factor in the overall cost of the plywood manufacturing operation, attempts have been made to reduce the adhesive usage as much as possible. Many of these attempts have involved the formulation of different types of adhesives and various additives which are intended to enhance the flow characteristics and/or the bonding properties. However, the different adhesive formulations that have been proposed are for the most part no better than the traditional phenolic, urea and various adhesives that have long been used, generally due to problems relating to cost, cure speed, bonding qualities handling difficulties and other factors.
One of the major contributing factors to excess adhesive usage is the tendency for significant portions of the adhesive to dry out prior to hot pressing of the plywood. A number of reasons exist for the dried glue lines, including low adhesive spreads, long assembly times, low moisture content veneers, excessive veneer temperature and excessive precure time before the hot press is closed. Whatever the reason, compensation for dried glue must be made by adding more glue, and the adhesive requirements are increased accordingly.